CSS, or Cascading Style Sheets, is a powerful language used to control the presentation and layout of HTML elements on a web page. By separating content from design, CSS allows developers to apply styles such as colors, fonts, spacing, and positioning to HTML elements, making it possible to create visually appealing and responsive web pages. With CSS, you can manage the look and feel of multiple web pages from a single stylesheet, ensuring consistency and efficiency in design. Its flexibility and wide range of properties enable you to enhance user experience, adapt designs for various devices, and create complex layouts with ease.